1. Field of the Invention
The present invention relates to a reference light source device using a laser diode.
2. Description of the Prior Art
Recently, light communications have widely been employed and the frequency band used in such light communications has become higher so as to enable transmission of an increased amount of information within the frequency band by means of frequency multiplexing.
A laser diode of the 1.5 .mu.m range has been widely used for light communications in terms of the transmission characteristics of optical fibers. Recently, it has been strongly required that light signals are stable and are precisely regulated at desired frequencies in order to perform optical frequency division multiplexing or heterodyne detection to improve the sensitivity of light signal reception. As is well known, the oscillation frequencies of laser diodes are very sensitive to driving currents and temperature. Hence, it is necessary to precisely regulate the driving currents and the ambient temperature of laser diodes. Generally, the laser diodes deteriorate with age, and the oscillation frequencies thereof may vary. In order to maintain constant the frequencies of the laser diodes, in the long term, it is necessary to employ a reference for the light signals practically used.